This invention pertains to water-dispersed polymers wherein amine functionality is generated in use to cross-link with reactive matrix polymers to form a cured cross-linked protective coating.
Amine functionalities are desirable in polymers for various reasons. Amine groups co-react with functionalities such as epoxide, isocyanate, isothiocyanate, double bond, etc., at room temperature. Room temperature cure of water-dispersed polymers is highly desirable by reason that environmentally undesirable solvents are avoided as well as energy sensitive heat curing processes are not necessary. Further, amine functional polymers frequently improve coating properties. When an emulsion polymerization is carried out using styrene, butyl acrylate and 2-amino ethyl methacrylate hydrochloride (2-AEM), it is found that about 95% of the amino-containing monomer polymerizes in the aqueous phase, and only the remaining 5% copolymerizes with styrene and butyl acrylate. However, this is not desirable for curing reasons. The small amount of homopolymer of 2-AEM will cure poorly. In order to have a good cure, the amino functionalities should be randomly distributed throughout the copolymer.
It now has been found that water-dispersed polymers with random distribution of amino functionalities can be prepared with an emulsion technique. This is achieved by blocking the amine with a ketone or aldehyde to form a ketimine and then co-polymerizing the ketimine monomers in an emulsion process at a controlled pH higher than about 7.2. At the high pH, the ketimine monomers and particularly the amino (--NH.sub.2) groups remain blocked to produce ketimine polymers useful later as cross-linker components in water-dispersed coatings. In use, the ketimine emulsion polymer is adjusted with acid to lower the pH below about 7 whereby amino (--NH.sub.2) groups on the ketimine polymer become unblocked and then become co-reactive with water-dispersed matrix polymers such as epoxy polymer, double bond polymer, or isothiocyanate containing polymer. The matrix polymer and the ketimine cross-linker polymers provide a surface coating composition which can be cured or cross-linked at ambient temperatures or temperatures not substantially above room temperature.